I know we already discussed something like this in another task, which IIRC about enforcing an assignee on tasks. After 2 months of use of Phabricator, I can confirm that enforcing an assignee is not requirement. However, having a default assignee for new tasks filed in a given project would help a lot. It's the easiest way to ensure tasks are looked at without having to enforce strict triage sessions (not practical for small projects).
We have a Phabricator extension to bounce back to the originator tasks created without any project. Finding projects is easy though, knowing who is the "lead" for each project is a lot more impractical. Using Herald rules for each project would be a lot of maintenance and would not scale either.